PHYSICAL SCIENCE: Chapter 13 Section 1 - Partial Work, Power and Machines

PHYSICAL SCIENCE: Chapter 13 Work & Power What is “Work” in physics? Work is ONLY done when a force causes a change in motion of an object and transfers energy to the object.

PHYSICAL SCIENCE: Chapter 13 Work & Power WORK is done when a person lifts something up (against the force of gravity. person pushes or pulls on a object (against the force of friction).

PHYSICAL SCIENCE: Chapter 13 Work & Power Frequently we use machines to lift and haul things. Those machines are helping do WORK.

PHYSICAL SCIENCE: Chapter 13 Work & Power So, while some people get paid to think up things at “work,” they aren’t really doing “WORK.”

PHYSICAL SCIENCE: Chapter 13 Work & Power In order for an object’s motion (or position) to be changed, a force has to be applied to cause the object to accelerate. The amount of “work” done can be calculated using the formula: WORK = FORCE x Distance = F x d

PHYSICAL SCIENCE: Chapter 13 Work & Power WORK is measured in units of Joules. WORK = Force x distance WORK = Newtons x meters 1 Joule (of WORK)= 1 Newton of force pushing or pulling on an object for 1 meter.

PHYSICAL SCIENCE: Chapter 13 Work & Power The amount of WORK done does NOT depend on how quickly the force causes the object to change its motion. The amount of POWER depends on how quickly WORK is done (we’ll cover POWER later).

1). If you push a wheelbarrow with a force of 250N for 15.5m, how WORK Calculations: 1). If you push a wheelbarrow with a force of 250N for 15.5m, how much work did you do? 2). A truck pulled a trailer 100.0m and did 50,500J of work. How much force did the truck supply? 3). It takes 695J of work moving a wagon. If you pull with a force of 375N, how far will it move?

PHYSICAL SCIENCE: Chapter 13 Work & Power WORK Calculations: 1). If you push a wheelbarrow with a force of 250N for 15.5m, how much work did you do? WORK = F x d WORK = 250.0N (15.50m) = 3875J

PHYSICAL SCIENCE: Chapter 13 Work & Power WORK Calculations: 2). A truck pulled a trailer 100.0m and did 50,500J of work. How much force did the truck supply? WORK = F x d 50,500J = F x (100.0m) 50,500J = F = 505N 100.0m

PHYSICAL SCIENCE: Chapter 13 Work & Power WORK Calculations: 3). It takes 695J of work moving a wagon. If you pull with a force of 375N, how far will it move? WORK = F x d 695J = 375N x d 695J = d = 1.85m 375N

PHYSICAL SCIENCE: Chapter 13 Work & Power Do Practice Problems (p. 432, 1-4) Show the formula, set up and answer with correct units

PHYSICAL SCIENCE: Chapter 13 Work & Power What is “POWER” in physics? POWER measures the RATE at which WORK is done.

PHYSICAL SCIENCE: Chapter 13 Work & Power POWER is calculated using the formula: POWER = WORK DONE = W TIME t POWER= Joules of Work = Watts seconds

PHYSICAL SCIENCE: Chapter 13 Work & Power POWER Calculations: 1). A crane lifts a steel beam 30.0m using a force of 3500.0N in 30.0s. a). How much WORK was done? WORK = 3500.0N x 30.0m WORK = 105,000J b). How much POWER was used? POWER = W = 105,000J = 3500W t 30.0s

PHYSICAL SCIENCE: Chapter 13 Work & Power Do Practice Problems (p. 434, 1-2) Show the formula, set up and answer with correct units

PHYSICAL SCIENCE: Chapter 13 Work & Power- Section 1 Mini-Quiz #1 1). What TWO things must happen for Work to be done? 2). What is the formula for Work? 3). What UNITS is Work measured in? 4). What UNITS is Power measured in?

PHYSICAL SCIENCE: Chapter 13 Work & Power- Section 1 Mini-Quiz #1 5). If you push a box for 6m with a force of 12N, how much Work was done? 6). If 27J of Work was done on a piano to move it 3m, how much Force was applied? 7). If 125J of Work was done in 5s, how much Power was used?

PHYSICAL SCIENCE: Chapter 13 Work & Power Team Mini-Quiz #1 1). What TWO things must happen for Work to be done? A force has to be applied on an object and the object must move. 2). What is the formula for Work? W = F x d 3). What UNITS is Work measured in? Joules

PHYSICAL SCIENCE: Chapter 13 Work & Power Team Mini-Quiz #1 4). What UNITS is Power measured in? Watts 5). If you push a box for 6m with a force of 12N, how much Work was done? WORK = F x d WORK = 12N x 6m = 72J

PHYSICAL SCIENCE: Chapter 13 Work & Power Team Mini-Quiz #1 6). If 27J of Work was done on a piano to move it 3m, how much Force was applied? WORK = F x d 27J = F x 3m 27J = F = 9N 3m

PHYSICAL SCIENCE: Chapter 13 Work & Power 7). If 125J of Work was done in 5s, how much Power was used? P = Work = W time t P= 125J = 25W 5s

PHYSICAL SCIENCE: Chapter 9 Work & Power: Machines Machines CAN: 1). Change the direction of an input force. In the case of a lever, you push DOWN to lift something UP.

PHYSICAL SCIENCE: Chapter 9 Work & Power: Machines Machines CAN: 2). Increase the amount of FORCE coming out of a machine to more than the FORCE being put into the machine.

PHYSICAL SCIENCE: Chapter 9 Work & Power: Machines When machines increase the FORCE coming out of a machine, it is called “multiplying the force.” BUT, Machines CANNOT reduce the amount of WORK required to lift or move something.

PHYSICAL SCIENCE: Chapter 9 Work & Power: Machines So, if machines get more FORCE out, but the WORK is the same, they must do the WORK over a longer DISTANCE.

PHYSICAL SCIENCE: Chapter 9 Work & Power: Machines When loading a crate on a truck, slightly less WORK is done by lifting the crate straight up (less distance), BUT, it takes a lot more FORCE to lift the crate than it does to slide it up a ramp, even when you have to push it further.

PHYSICAL SCIENCE: Chapter 13 Work & Power Mini-Quiz #2 1). What 2 things can a machine do to make Work easier? 2). What can a machine do to reduce the amount of Work?

PHYSICAL SCIENCE: Chapter 13 Work & Power Team Mini-Quiz #2 1). What 2 things can a machine do to make Work easier? “multiply” the input force and change the input force direction. 2). What can a machine do to reduce the amount of Work? It can’t reduce the amount of Work needed to be done.

PHYSICAL SCIENCE: Chapter 13 Work & Power Team Mini-Quiz #2 3). What is the definition of M.A.? The number of times that the INPUT FORCE is “multiplied” 4). What is the formula for ACTUAL M.A.? A.M.A. = output Force = Fout input Force Fin 5). What does ACTUAL M.A. consider that Ideal MA doesn’t? FRICTION

PHYSICAL SCIENCE: Chapter 13 Work & Power Team Mini-Quiz #2 6). If you lift a log and applied 2000N of force, but a machine could do it with 1500N, what is the A.M.A of the machine? A.M.A. = output Force = Fout input Force Fin A.M.A. = 2000N = 1.33 1500N

PHYSICAL SCIENCE: Chapter 13 Work & Power THINGS TO KNOW 1). What two things have to happen for Work to occur? 2). What is the Work formula? 3). What units are used for Work? 4). Be able to calculate Work. 5). What is “Power?” 6). What is the formula for Power?

PHYSICAL SCIENCE: Chapter 13 Work & Power Chapter 13, Section 1 QUIZ 1). What two things have to happen for Work to occur? 2). What is the formula for Power? 3). What are the UNITS for Work? 4). What are the UNITS for Power? 5). How much Work is done by rolling a ball 25m with 12N of force?

PHYSICAL SCIENCE: Chapter 13 Work & Power Chapter 13, Section 1 QUIZ 6). How much Power is used by rolling a ball 150m with 6N of force in 300s? 7). How much Power is used by carrying a 600N box 15m up some stairs in 30s?